He is expected to inform the king of his decision after chairing his last cabinet meeting at 10am (02:00 GMT).
Afterwards, Mohamad Redzuan Yusof, a minister in the prime minister’s department, told online newspaper Malaysiakini that Muhyiddin had told the party he planned to resign the following day.
The political upheaval comes amid rising public anger at the continued surge in coronavirus cases despite months of various levels of lockdown.
Many Malaysians blame the government for spending too much time on politics and not enough time governing.
Some 12,510 people have died from the disease as overloaded government hospitals struggle to cope.
On Sunday, Malaysia recorded 20,546 cases on Sunday, its fourth successive day of more than 20,000 cases.
Who is Muhyiddin Yassin?
Muhyiddin, 74, is a veteran politician who began his career with the United Malays National Organisation (UMNO) before jumping ship amid the tumult of the multibillion-dollar 1MDB scandal in 2015.
He became prime minister in March 2020, after a week of political turmoil triggered by a power grab within the then-ruling Pakatan Harapan coalition that led to the resignation of his predecessor, Mahathir Mohamad.
Following days of uncertainty, Muhyiddin convinced the king he had sufficient support among members of parliament to form an administration.
His Perikatan Nasional (PN) coalition included his own Bersatu party – without founder Mahathir and his supporters – defectors from the previous administration’s Parti Keadilan Rakyat, as well as UMNO, Parti Islam Se Malaysia or PAS, the country’s Islamic party, and GPS, the ruling party in the Borneo state of Sarawak.
Muhyiddin’s cabinet included 70 people, the largest in Malaysian history, with four “senior ministers”. Some politicians were also appointed to prominent roles in government-linked businesses.
What went wrong?
Muhyiddin’s support and legitimacy have been questioned ever since he came to power.
As a result of a pandemic lockdown, it was not until July 2020 that parliament sat for the first time following the change in government. Muhyiddin survived a delayed budget vote with a majority of just two.
Opposition leader Anwar Ibrahim has claimed a number of times he has the support to rule but it is UMNO that has proved to be Muhyiddin’s biggest headache.
Part of the country’s political landscape since it was founded in 1946, the PN-era saw an emerging split in the party’s upper echelons.
While those holding prominent positions in the cabinet backed the status quo, other senior members – including UMNO President Ahmad Zahid Hamidi and former Prime Minister Najib Razak – were more critical. Zahid is on trial on a slew of corruption charges while Najib was found guilty in the first of a series of 1MDB-linked trials in 2020.
Since September last year, the party has announced its withdrawal of support for Muhyiddin a number of times.
In July, hours before Zahid was expected to announce the party would no longer back him, Muhyiddin promoted Ismail Sabri Yaacob and Hishammuddin Hussein, the two most prominent UMNO politicians in his cabinet to senior roles. Sabri was named deputy prime minister.
What about COVID-19?
Shortly after taking power, Muhyiddin imposed a strict lockdown that proved largely effective in controlling the coronavirus.
Restrictions were slowly lifted and in July 2020, the country announced zero cases.
But an outbreak had begun to pick up in the Borneo state of Sabah, where PN politicians began to move against the state government – aligned to the previous Pakatan Harapan administration.
A state election was called for September and politicians flew backwards and forwards between Sabah and Kuala Lumpur without being required to quarantine.
The result was a surge in cases that led to new restrictions being imposed in October. The rules were relaxed again just before the Christmas and New Year holidays – a popular time for travel in Malaysia – and in January cases surged again.
Muhyiddin, under increasing pressure politically, then announced he had secured the king’s backing for a state of emergency in order to battle the pandemic. The decision also suspended parliament.
Since then, cases have continued to rise, triggering what Muhyiddin called a “total lockdown” in June when the country was reporting 7,000 cases a day.
The prolonged disruption to business and schooling, coupled with a lack of financial support, has heightened anger among many Malaysians.
There have been protests by young people, a strike by junior doctors and a grassroots campaign to provide assistance to those most in need.
“It is evident that the current strategy is not working, and the current administration has failed,” IMAN, a Malaysian think-tank, said in a statement on Sunday. “A new strategy and a new leadership are urgently needed.”
One of the few bright spots, has been a noticeable acceleration in the country’s vaccination programme following a sluggish start. Some 32.9 percent of the population have now had two shots, according to the government.
Who could take over?
It is not clear who could emerge as the country’s next prime minister, given the fluid state of political loyalties.
The ructions could see UMNO’s return to the pole position.
Among those in the frame are Ismail Sabri, despite his prominent role in handling the pandemic.
Tengku Razaleigh Hamzah, a veteran UMNO leader, is also said to be a possibility.
On the opposition side, Anwar Ibrahim, may see this as his last chance to be prime minister, a position which has long eluded him.
Rather than focussing on who should be the next prime minister, the opposition Democratic Action Party (DAP) said politicians should be looking at an effective COVID-19 ‘reset plan’, measures to support the economy and institutional reform.
What about the king’s role?
Malaysia has a unique system of monarchy where the role of king is rotated every five years among the nine Malay sultans.
The current monarch, King Al-Sultan Abdullah, is from the central state of Pahang and took the throne in 2019.
It is a constitutional monarchy, but the king has become increasingly prominent since Muhyiddin took charge.
He met each member of parliament individually before being convinced Muhyiddin had the support to form a government but also rejected Muhyiddin’s first request for an emergency last year.
In June, amid the deepening COVID-19 crisis and continued political manoeuvring, he called for parliament to sit “as soon as possible”, repeating the call two weeks later.